1. Field of the Invention
This invention is directed to a background noisemasking system which employs a single noise generator and equalizer in connection with a plurality of time delays to feed an equalized noise signal to different speaker arrays with different time delays.
2. Description of the Prior Art
Designers of large office operations have abandoned the practice of placing each desk in its own small room. Instead, today's office arrangement concept is to provide spacious open floors which are shared by many desks. The new concept, when employed to its greatest advantage, affords better efficiency and an informal atmosphere; however it is desirable to retain one property which is automatically provided by small or individual offices. This property is the privacy of conversation. The conversation may be with another worker or on the telephone. The protection of each worker from the distracting intrusion of noises from adjacent sources, such as conversations, business machines, and telephone ringing is a critical factor detrimental to this design. The open plan concept has gone beyond the office and is finding acceptance in hospital patient rooms. The specific details of the problem differ from the office requirements, but the basic goal is the same. In the hospital ward, each patient should be isolated from the sounds of the other patients, their conversations, and TV sets. In schools, the problem is more difficult because one large room may be shared by several classes of students. Each class must be acoustically coupled within itself, but each class must be acoustically separated from the adjacent one.
The use of sound-absorbing acoustical material is a basic element in the design of such spaces. Use of carpeting and wall and ceiling acoustical surfaces is common. In addition, panels and sound barriers are individually arranged to aid in the separation of spaces; however these measures cannot provide an adequate solution.
Most of the open-spaced offices are defined above by a ceiling, and above the ceiling is a plenum in which the offices services are channeled. Sprinkler piping, water piping, air-conducting duct work, electrical conduits, and the like are routed through the plenum space.
The prior art provides background masking noise, but the noise must be uniformly distributed through the space in order to achieve the satisfactory end results. If the noise is not uniform, masking is ineffective in one area, and a person walking through the room would be subjected to different intensities of background noise and thus would become conscious of it. The prior art systems mostly utilize commercial sound system components and then use sound contractors to install the loudspeakers in the plenum space above the open plan office ceilings. The plenum space above the ceilings is usually cluttered with air-conditioning ducts and electrical conduits. The speakers are positioned so that the plenum space is utilized as a mixing chamber for the background noise and, in theory, the noise filters down uniformly through the ceiling and into the office space; however this is only potentially true when the plenum is unobstructed and acoustically hard. The insulated air-conditioning ducts and the other equipment in the plenum interfere with this distribution and thus the plenum does not act as the theoretically uniform mixing chamber. Now, individualized positioning of the speakers by field acoustic technicians is required in order that the masking sound be uniform in the office space below.
The invention described above in the cross-reference is directed to the use of two independent noise sources feeding two sets of loudspeakers in an array, together with a third channel which is derived as the sum or difference of the two independent noise sources. The psycho-acoustic result of this arrangement is that a person exposed to the sound field produced by this arrangement feels immersed in a sea of sound. This is also the desired result of the present system wherein the result is accomplished in another way.